The present invention relates to a vacuum pump apparatus, and, more particularly, to a non-lubricated vacuum pump apparatus which does not employ oil for cooling and lubrication in a working space and which is suitable for handling corrosive gas used in producing semiconductor devices or gas in which a reaction product is produced. The present invention also concerns a shaft sealing device for this pump apparatus.
When gas suctioned and exhausted by a vacuum pump is corrosive gas or noxious gas containing dust, or the like, a means is available for introducing inert gas into an internal housing in order to protect a drive apparatus such as a motor or a wiring therefor from being corroded by the gas, as disclosed in Japanese Patent Unexamined Publication No. 61-43298.
Meanwhile, in a vacuum pump, a working space is separated from a bearing chamber or a gear chamber by providing a non-contact type shaft sealing device, as disclosed in U.S. Pat. No. 4,714,418. Accordingly, measures are taken to reduce a pressure difference across the shaft seal so as to reduce the shaft sealing load.
In non-lubricated screw vacuum pumps, bearings supporting a male rotor and a female rotor are disposed on both sides of the rotors and a timing gear is provided for synchronizing the rotation of both rotors. Hence, it is necessary to prevent the oil which has lubricated these portions from entering the working space. If such a screw vacuum pump is used for an apparatus for producing semiconductors as a pump for handling corrosive gas or gas in which a reaction product is produced, it is necessary to take protective measures against the corrosion and reaction products in the shaft sealing device, the bearing chamber, and the gear chamber. Particularly, since the concentration of the gas is high in the gear chamber on the discharge side, the discharge side of the gear chamber is subjected to severe conditions as compared with the suction side thereof.